Rainbows can be formed by droplets of liquids other than water, or even by a cloud of solid transparent microspheres. The table below shows the viewing angles for primary rainbows produced by a number of different media.
|Other glass||1.47 to 1.61||25.7 to 14.2|
Primary rainbow viewing angles for various media
- Materials with an index of refraction of 2.00 or more do not produce primary rainbows.
- Diamonds, for example, do not produce primary rainbows because their index of refraction is 2.42. However, if a diamond is ground into microspheres, it can produce secondary and higher-order rainbows.
Data from https://www.basic-physics.com/rainbows-figuring-their-angles/